Adicao de bibliotecas I2C para DS1307 (funcoes reduzidas) conforme licensa GPL abaixo:
(ds1307 lib 0x01, copyright (c) Davide Gironi, 2013, Released under GPLv3)
(arquivos ds1307.c, ds1307.h, i2cmaster.h)
(I2C master library using TWI interface, twimaster.c, v1.3 2005/07/02)